“Stimulation is anything that wakes up the nervous system, gets its attention, makes the nerves fire off another round of the little electrical charges that they carry. We usually think of stimulation as coming from outside, but of course it can come from our body (such as pain, muscle tension, hunger, thirst, or sexual feelings) or as memories, fantasies, thoughts, or plans. Stimulation can vary in intensity (like the loudness of a noise) or in duration. It can be more stimulating because it is novel, as when one is startled by a honk or shout, or in its complexity, as when one is at a party and hearing four conversations at once plus music. Often we can get used to stimulation. But sometimes we think we have and aren’t being bothered, but suddenly feel exhausted and realize why: We have been putting up with something at a conscious level while it was actually wearing us down. Even a moderate and familiar stimulation, like a day at work, can cause an HSP to need quiet by evening. At that point, one more “small” stimulation can be the last straw.”